If history is any indication, history isn't any indication. (E.g., Apple is always the niche player, right?)
Just because the previous top social network eventually faded away doesn't mean we should expect the current one to do the same in any similar manner or time frame. There's quite a lot that differentiates today's Facebook and the MySpace of old. For one thing, how many third parties ever built on MySpace as an application platform, to the extent that they are today with Farmville and Microsoft Docs and the like?
Just because the previous top social network eventually faded away doesn't mean we should expect the current one to do the same in any similar manner or time frame. There's quite a lot that differentiates today's Facebook and the MySpace of old. For one thing, how many third parties ever built on MySpace as an application platform, to the extent that they are today with Farmville and Microsoft Docs and the like?